Insulator



' 6 4 f CROSS'REFERENCE M. H. HUNT INSULATOR Filed Jan. 22. 1931 Sept. 11, 1934.

" Silk-a2: glaze,

- 4 Comb/bed 5T/fcafe A? Mefal/fc glaze.

Silicazbg/azc INVENTOR WITNESSES. j 54 Mansaen H. Hu'nf' ATTORN EY EXAMIN Patented Sept. 11, 1934 UNITED STATES PATENT OFFICE 1,973,076 msum'roa Application January 22, 1931, Serial No. 510,443

My invention relates to insulators and particularly to insulators having semi-conducting surfaces.

One object of my invention is to provide a permanent lustrous body that shall have a core or body of dielectric material and a coating of intermediate conductive-resistive character, in homogeneous or molecular joinder thereto.

Another object of my invention is to provide an insulator coating that shall be more readily adapted to have one of awider variety of conductive-resistive values than similar coating heretofore employed.

Another object of my invention is to simplify the provision of frangible or inorganic dielectricbodies, of material such as porcelain, having coatings of higher conductivity than the bodies.

Another objectof my invention is to prevent energy losses and radio interference incident to certain electrical apparatus.

A further object ofmy invention is to provide an insulator or resistance element that shall be simple and durable in construction, economical to manufacture and effective in its operation.

Heretofore, it has been suggested to coat dielectric bodies, of material such as porcelain, with a highly-conducting material, or with a material of a conductive-resistive value between the socalled highly-resistive value of the bodies and the highly-conductive value of the conductors or cables with which they cooperate. These expedients have been suggested for various purposes, such as for reducing radio-interference and energy losses, and for inserting resistance directly in a circuit.

Aside from the earlier suggestions of providing the insulators with sheet-metal shields, which are expensive and difficult to manufacture, and have other objections, some of the later suggestions embody the application of plastic or fluid materials which are difficult to app to a hard, brittle dielectric, like porcelain, and, also, limit the variety of grading eifects which may be obtained.

It has been suggested to coat porcelain insulators with metallic glaze, a substance which can be applied in the liquid state and .flred to constitute a permanent, lustrous highly-conducting surface film. This glaze, alone, is subject to deterioration by abrasion, and from the effects of electrostatic streamers, and further provides a sharp break between its outer edge and the adjacent dielectric surface. The above defects can be overcome, as by coating the glaze and placing a graded-resista11ce coating next to its outer edge.

A suggestion embodying the placing of a semiconducting cement on a porcelain insulator, near the conductor which it supports, would not appear to be practicable, effective or permanent.

Other structures embodying the firing of car- 00 bon particles into the silicate glaze surface, or placing metal compounds on the insulator 'surface and reducing them, have been suggested, but they do not have the advantages of my invention, which comprises the simple expedient of mixing 66 metallic and silicate dielectric glazes while still in the wet state and applying the mixture to the insulator surface for firing. By this procedure,

a wide variety of mixes are obtainable, with the result that substantially any desired degree or 70 grading of conductivity, through the medium of a permanent lustrous glaze may be had.

Figure 1 of the accompanying drawing is a view. in side elevation, of a multi-part pin insulator embodying my invention, and

Fig. 2 is an enlarged detail view, in section, of a portion of the device of Fig. 1.

The insulator, which is merely illustrative of one of many applications of the invention, comprises a terminal portion having a cable-receiving groove 2 and a tie-wire groove 4, an upper petticoat or surface-creepage portion 6, a body 8 and a lower petticoat 10.

The terminal portion is preferably completely covered by a highly-conducting coating down to a circular line 12 on the petticoat 6, and, from the line 12 to a line 14, the petticoat is covered by a semi-conducting coating of my invention. The remainder of the insulator, below the line 14, is preferably covered by a usual silicate glaze, although the coatings may be readjusted and arranged in various ways in accordance with different conditions.

As shown more clearly in Fig. 2, the porcelain body of the insulator is preferably first entirely covered on its exposed surface with a usual silicate-glaze coating. A preferred silicate glaze, known as maho an laze, contains, approximately, Alban sii felds ar 5%, flint 5%. {Egg 3% and Mug; 2%. THE glaze is of Highly ulating character.

Next, and upwards from the line 12, the metallie-glaze coating is applied. A preferred metallic glaze comprises, in addition to the essen'tialoll's "GIIaVender and spike, about 1.85% fifet'iillicresp 1-1 e jbhtaining"approximately 43% platinum, 3.1% 19 .11: 3% bain g n, in the forms of chlorides o'r metals, and about 1% insoluble reiidu e. "rn-rs'giaze is of highly conducting'chai-acter.

The semi-conducting coating of combined silicate and metallic glaze is applied between the lines 12 and 14 and fired simultaneously with the upper metallic-glaze coating. After this operation, the metallic-glaze coating may be, and preferably is, covered by a solder coating or other protective means.

The result is an insulator having a permanent lustrous homogeneous coating of different degrees of conductivity, decreasing downwardly from the upper terminal portion to the substantially purely dielectric silicate-glaze coating below the line 14.

The zone between the lines 12 and 14 may be of difierent degrees of resistivity in the same or different insulators,- depending on whether it is made of one or more mixtures which, while in the fluid state, may be applied as desired.

In operation, since the cable and tie wire are in good contact with the solder coating, which is, in turn, in autogenous Joinder with the homogeneously united metallic glaze, silicate glaze and porcelain bodies, there is no electrostatic discharge adjacent to the cable and tie wire, and, since the mixture or resistance coating, between the lines 12 and 14, is next to the exposed silicate coating below it, the discharge is also eliminated or reduced to a negligible quantity at the line 14, thus eliminating energy loss and preventing radio interference from this cause.

While I have shown and described a particular form of my invention, changes may be made therein without departing from the spirit and scope thereof, as set forth in the accompanying claims.

I claim as my invention:

1. In combination, an inorganic dielectric member, a fired silicate-glaze coating thereon and a fired high-resistance surface coating over said first coating comprising a mixturepf a silicate and a metallic glaze said coatings being mechanically integral.

2. In combination, a porcelain body, a fired surface coating thereon of silicate glaze and a fired high-resistance surface coating over said first coating comprising a mixture of a silicate and a metallic glaze said coatings being mechanically integral.

3. In combination, a porcelain body having a terminal portion and a surface-creepage portion adjacent thereto, a silicate-glaze coating on both of said portions, a metallic-glaze coating on said terminal portion over said first coating and a coating over the silicate-glaze coating of, said surface-creepage portion and comprising a mix- I ture of a silicate and a metallic glaze.

4. In combination, a porcelain body having a terminal portion and a surface-creepage portion adjacent thereto, a silicate-glaze coating on both of said portions, a metallic-glaze coating on said terminal portion over said first coating, a metal coating over said metallic-glaze coating and a coating over the silicate-glaze coating of said surface-creepage portion and comprising a mixture of a silicate and a metallic glaze.

5. A graded dielectric member comprising an inorganic dielectric body portion having a surface coating over an area thereof consisting of a fired silicate glaze, and a second surface coating over an area contiguous to said first mentioned area consisting of a'fired mixture of a silicate glaze and a metallic glaze, said surface coatings being mechanically integral. j

8. A graded dielectric member comprising an inorganic dielectric body portion having a surface coating over an area thereof consisting of a silicate glaze, a second surface coating over an area contiguous to said first mentioned area, said 'second coating consisting of a fired mixture of a silicate glaze and a. metallic glaze, and a third surface coating over an area contiguous to said second mentioned area, said third coating consisting of a fired metallic glaze, said surface coatings being mechanically integral.

7. The'method of preparing a graded coating for an inorganic dielectric member which comprises coating a large surface of the member with a silicate glaze, firing the g1aze,-coating a portion of the large surface with a mixture of a silicate glaze and a' metallic glaze, and firing the mixture, whereby an integral coating having substantially homogeneous mechanical properties and graded electrical properties is produced.

8. The method of preparing a graded coating for an inorganic dielectric'member which comprises coating a large surface of the member with a silicate glaze, firing the glaze, and sub-- sequently applying and firing two coatings to contiguous portions of the large surface, the said two coatings comprising a metallic glaze and a glaze consisting of a mixture of silicatefglaze and a metallic glaze, whereby an integral coating having substantially homogeneous mechanical properties and three portions of graded specific resistance is produced.

MARSDEN H. HUNT. 

